The present invention relates to sprinkler units and pertains particularly to a special reversible drive gear system for oscillating sprinklers.
In my prior U.S. Pat. No. 3,107,056, issued Oct. 15, 1963, entitled "SPRINKLER", I disclose a gear driven oscillating pop-up type sprinkler. In that patent, the drive train includes a shifting mechanism that alternately shifts a pair of terminal gears carried on a shifting plate or carrier into and out of engagement with an internal gear at the ends of the oscillating stroke. In adapting that drive system to more compact higher pressure, higher volume pop-up sprinklers, certain problems with the shifting mechanism were encountered.
The chief difficulty encountered was the different engaging and shifting forces present in the shifting mechanism. The shifting mechanism has a very strong self-engaging force when turning in the same direction as the input drive. A great deal of force is required to disengage the drive and shift to the opposite direction. This problem was solved in my U.S. Pat. No. 4,568,024, issued Feb. 4, 1986, entitled "OSCILLATING SPRINKLER".
However, a new problem has been discovered, namely when the sprinkler unit is shut off and stops while in the process of shifting from one direction to the opposite direction, the terminal gear becomes disengaged from the ring gear. When the water is again turned on, the drive remains disengaged and will not function. The sprinkler unit is then thought to be defective by the user or consumer and is typically discarded or returned to the vendor for replacement.
It has been discovered that the lost motion connection between the shifting arm and the carrier allows the shifting arm to be biased to a position short of the over-center position, such that the carrier allows the terminal gear to become disengaged. This condition can also occur when the sprinkler head is turned manually to check or adjust the coverage. This problem has been solved to a great extent by a third over-center biasing spring acting on the shift lever as disclosed and claimed in my U.S. Pat. No. 4,718,605 entitled "REVERSIBLE GEAR OSCILLATING SPRINKLER", granted Jan. 12, 1988. However, a simpler and more economical solution is desirable.
It is, therefore, desirable that an improved gear drive be available for sprinkler units that overcomes this problem.